RU2397850C1 - Procedure for fabrication of flat bi-metallic work-piece by explosion welding - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be implemented at fabrication of flat bi-metallic work-pieces out of dissimilar metals. A thrown plate is positioned with a gap over a stationary plate; there is initiated discharge of explosive substance located over the thrown plate. To damp speed of plastic deformation damping devices are placed under the stationary plate in form of an easily deformed interlayer possessing property of one-sided non-flexible deformation and in form of an artificial support platform. The platform is made out of material with uniformly distributed density exceeding density of the easily deformed interlayer.

EFFECT: upgraded quality of produced bi-metallic work-piece.

3 cl, 2 dwg

Description

The invention relates to metallurgy and can be used in the manufacture of flat bimetallic billets from dissimilar metals.

Explosion welding is a technological process that allows to obtain bimetallic billets and products of almost unlimited sizes from a variety of metals and alloys, including those whose welding by other methods is difficult. Thus, obtaining large-sized bimetal blanks titanium-steel, aluminum-steel, zirconium-steel and many others is possible only by explosion welding.

Explosion welding refers to a type of pressure welding when pressure is created by the detonation products of an explosive (hereinafter - EXPLOSIVES). Connecting parts, for example plates, one of which is stationary (clad plate), is located at a certain distance (or at a certain angle) from each other. An explosive with a detonator is placed on a moving part (a missile, clad plate). When the detonator is triggered, the process of decomposition of the explosive occurs, creating a pressure that propagates behind the detonation front.

A decisive role in the formation of a welded joint is played by the plastic deformation of the metal in the heat-affected zone, which is distributed exponentially over the thickness of the parts to be welded and reaches hundreds of percent near the joint line.

Due to the short formation time of the welded joint, insufficient for the flow of active diffusion processes at the interlayer boundaries, the explosion welding method has the unique capabilities of joining alloys and metals that are not welded by conventional methods.

As a rule, high-quality joining of metals is achieved by observing the exact balance between the supplied kinetic energy of the propelled plate and the absorbed energy spent on the necessary and sufficient joint plastic deformation of the mating surfaces of the propelled and fixed plates.

With a lack of energy, a qualitative continuous compound or compound does not occur at all, with an excess of energy, the excess part is spent on endothermic reactions of the formation of foreign inclusions (carbides, nitrides, intermetallic compounds), the formation of fusion zones at the interface and the deformation of the plates themselves.

To relieve stresses arising from explosion welding, tempering of the finished product is used, as a result of which the strength of the connection inevitably decreases and the greater the greater the content of the melts.

Test methods and evaluation of the microstructure, for example, for steels are regulated by the standard - GOST10243-75.

The most problematic is the connection of metal pairs with significantly different melting points, such as steels and aluminum alloys, steels and hard bronzes and brass, steels and titanium alloys.

The melting temperature of steels is at the level of 1530 ° С, the melting temperature of aluminum alloys is at the level of 660 ° С, of bronzes and brass - 85 ÷ 1000 ° С, while the strength of the clad metal is close to or exceeds the strength of the steel with which the connection is made. With this combination of properties of the metals being joined, an inevitable significant melting of the metal with a lower melting point occurs.

For this reason, for example, compounds of steel and aluminum alloys of grades AMg5, AMg6 are not industrially produced by explosion welding, since during explosive conjugation of the plates, the crystal lattice of the aluminum alloy is completely destroyed and a significant part of the metal passes into the melt, the cooling time of which is several times longer than the duration of the detonation products of any known explosives and mixtures.

Thus, in order to obtain structural bimetal with high operational and strength properties, it is necessary to absorb excess energy and achieve an energy balance between the input and absorbed energy to obtain strictly dosed plastic deformation of the mating metals.

Known explosives do not allow the wide variation of the time and speed of detonation products and do not successfully solve this problem and, accordingly, ensure high-quality welding of metals with an unfavorable combination of physical and mechanical properties in industrial production.

A known method of cladding by explosion welding, including cleaning the welded surfaces of the clad and clad (thrown) metal sheets, installation on the remote supports of the clad sheet above the clad sheet at a distance of the welding gap, the layout on the clad sheet of the explosive charge layer with the initiation system (see patent RU No. 2237558, B23K 20/08, F42D 5/045, 2004).

The method further comprises laying out a first layer of bulk material on an explosive charge layer and above it a second layer of bulk material or a water layer through an air gap, initiating an explosive charge and welding the clad and clad sheets with explosive energy. Moreover, the thickness of the first layer of bulk material is assumed to be from 1 to 3 thicknesses of the explosive charge layer, the second layer of bulk material or water layer - from 3 to 5 thicknesses of the explosive charge layer, the air gap - from 2 to 4 thicknesses of the explosive charge layer.

The disadvantage of this method is that it does not give a positive effect if the dissimilar metals of the connected plates have significantly different melting points, since in this case, due to increased pressure and the duration of its action, the probability of extensive melting increases.

There is also a known method of explosion welding, based on the installation with a gap of the missile plate above the fixed plate and the initiation of the explosive charge located above the missile plate (see patent RU No. 2243871, B23K 20/08, 2005).

Moreover, the surfaces of the welded plates are pretreated to a roughness Rz equal to 8.0 ÷ 42.0 μm, and the welding is carried out by the pressure of detonation products, the action time of which exceeds the cooling time of the surface layers of the plates melted to a depth of more than 2 μm.

The method allows to reduce the level of loads required to accelerate the missile plate (there is no need to provide a high impact speed necessary to exceed the yield strength of the material).

However, with this method, welding of the mating surfaces of the plates is achieved by melting them, which negatively affects the structural strength of such a connection, since the melt is a foreign structure with respect to the metal structure of both plates.

A known method of explosion welding for the manufacture of multilayer compounds of aluminum alloy, pure industrial aluminum, silver plate and stainless steel (see JP patent No. 9029463, B23K 20/08, 1997).

In this technical solution, pure aluminum is used to absorb shock.

The disadvantage of this method is the limited scope of such a solution, since the components of the compound are negotiated and cannot be used for other bimetals.

There is also a known method of manufacturing metal composite materials processed at high temperatures (see US patent No. 2005104638, B23K 20/08, 2001).

This method allows to prevent the formation of brittle intermetallic compounds due to the use of an additional layer of tantalum or niobium that do not form intermetallic compounds.

However, the known method is technically complicated and expensive, it does not allow to obtain bimetallic sheets of large area.

A known method for producing a composite steel-aluminum adapter, including explosion welding of a steel clad sheet with two clad aluminum sheets (see patent RU No. 2270742, B23K 20/08, 2006).

In this case, the cladable steel sheet is pre-chrome plated to obtain a layer with a thickness of 0.03 ÷ 0.07 mm, and when welding the first clad sheet, the charge is placed in a closed container, divided in the direction of the detonation front into separate rectangular sections with a width of not more than two charge heights .

This technical solution helps to stabilize the speed of detonation of explosives near its minimum value, which allows to improve the quality of steel-aluminum adapters, however, the method has limited application.

The closest in technical essence to the claimed solution is a method of manufacturing by explosion welding of a composite material consisting of a fixed part (substrate), an intermediate layer of metal compatible with the substrate material, and a missile part (shell) (see patent WO No. 20044060599, B23K 20 / 08, 2004).

The method includes placing welded parts with a gap between them, placing an explosive charge above the upper part, using an additional intermediate layer (means) to mitigate the impact of the explosion, and initiating an explosive charge.

This method allows you to create a flat interface between the elements of the welded structure, prevents the occurrence of harmful waves that form cracks in this structure, as well as the formation of intermetallic inclusions on the interface.

The disadvantages of the known solution is that the intermediate layer, which softens the effect of the explosion, remains an integral part of the resulting bimetallic compound and is a “weak” element of the composition that reduces the operational characteristics of the bimetal, there are also restrictions on the size of the welded parts and the difficulty of placing the intermediate layer in the manufacture of large-sized blanks.

An object of the invention is the creation of a new method of manufacturing bimetallic billets with high characteristics of strength and quality of the welded joint for metals with significantly different melting points.

The technical result of the proposed solution is to improve the quality of the connection of the workpiece parts by reducing the impact energy acting on the mating surfaces by compensating for the elastic deformation and limiting the amplitude of the elastic vibrations acting on the part from the moment of their first contact until the end of the pressure wave.

To achieve the specified technical result in the method of manufacturing by explosion welding of a flat bimetallic billet based on the installation with a gap of the projectile plate over the fixed plate and the initiation of an explosive charge located above the projectile plate, including the use of additional means to reduce the rate of plastic deformation of the plates, according to the proposal as add-ons use a damping agent made under a fixed plate and consisting of easily defo ble layer having property sided inelastic deformation and an artificial support pad made from a material with uniform density exceeding the density of readily deformable layer.

Also, according to the proposal, an easily deformable interlayer having the ability to change the state of aggregation under pressure is used, and at least one additional damping interlayer is placed between the easily deformable interlayer and the support platform.

It was experimentally established that the inventive method, firstly, allows you to compensate for the elastic compression of the plates that come into contact and their subsequent elastic expansion, which “tends” to break the connection that has arisen, finding a “weak spot” in it.

In most cases, such a “weak spot” is an unhardened melt or its oxidized (due to too high temperature for a more fusible metal) surface.

Secondly, the inventive method makes it possible to limit the amplitude of the elastic vibrations acting on the plates from the moment of their first contact to the end of the action of the pressure wave.

Together, these two factors provide a reduction in the impact energy acting on the mating surfaces to a level that excludes extensive melting of the mating surfaces, and significantly limit the formation of carbides, nitrides, and intermetallic compounds, and, as a result, endothermic reactions at elevated temperatures.

Compensation of elastic deformation allows the most effective joint plastic deformation of the surfaces of the welded plates due to the smooth increase of the pressure pulse, increase of its duration and elimination of the simultaneous action of the processes of elastic expansion and elastic vibrations.

The presence of a damping agent, consisting of an easily deformable layer (hereinafter referred to as LDP), which has the property of one-sided inelastic deformation, and a support pad of a material with a higher density, leads to the fact that the derivative of the rate of plastic deformation does not change sign over the entire duration of the pressure pulse until its end. The duration of the pressure pulse is delayed by the time of deformation (destruction) of the interlayer, and the amplitude of the pulse decreases. The mutual arrangement of the welded plates and the damping means is schematically shown in figure 1.

To confirm the effectiveness of such a solution, we give estimated values of the time course of the processes that make up the explosion welding method as a whole, obtained in accordance with the methodology described in the book "Explosion welding", V.I. Lysak, S.V. Kuzmin. M .: "Engineering-1", 2005, pp. 23-29.

The duration of formation of the compound as a whole is 10 ^-6 s.

The condition for obtaining a durable high-quality joint in explosion welding, taking into account the main process parameters and the properties of the materials being welded, is represented by the expression

tv> ta≥tp,

where tv is the interaction time (action of contact stresses);

ta is the surface activation time (depends on the properties of the atoms that make up the crystal lattice), it is estimated that ta is 10 ^-8 ÷ 10 ^-7 s;

tp - relaxation time, estimated as tp equal to 10 ^-7 s.

The vertical collision velocity of the plates is estimated on average as Vb is 500 m / s.

When using an easily deformable interlayer (for example, from polyethylene foam, etc.) with a thickness of 1 ÷ 2 mm, the time of final compression of the plates increases by 2 × 10 ^-6 ÷ 4 × 10 ^-6 s, which fully satisfies all conditions and is easily implemented.

In this case, there is no peak pressure as a result of instantaneous braking on a tight barrier. At the same time, the compression and subsequent expansion shift in phase, which leads to significant energy losses, and the amplitude of the reverse expansion drops to a level safe for the welded joint. Already having one easily deformable layer is enough to provide a new qualitative level of the explosion welding process.

The experiments showed that additional possibilities for ensuring continuous contact of the welded plates while maintaining the pressure level achieved in the pulse are provided by the use of an active layer that ignites under the influence of a pressure pulse. In this case, both plates are under the influence of gaseous product pressure both from the side of the cladding and clad material. The gas damper organized in this way acts even more “softly”, which is especially important for high-strength and low-melting materials, for example AMg6.

It was also solved the problem of maintaining the achieved level of welding quality until the completion of the existing factors and quenching the kinetic energy of the finished product as a whole and each of its parts separately, since there are no ideally flat plates. The standardized permissible deviations from flatness are usually 5 mm per meter of plate, which is almost the same as the size of the commonly used gap between the plates.

Thus, the sections of the plates spaced from the conditional midline of each of them, as a result, acquire more or less acceleration.

The collision speed in real conditions is different for each section of the area of the welded plates.

Forced deformation of shape distortions leads to "conservation" of randomly directed elastic stresses acting tangentially in the plane of welding of the plates. Therefore, it is necessary to maximally compensate for the effect of these secondary factors, in relation to the actual welding of two surfaces.

Under an easily deformable layer, we carry out a support platform of a higher density material.

As a rule, planned ground, rocky foundation, massive concrete or metal slab, which also do not have perfect shape, are used as a supporting platform. In the first case, the reference pad is heterogeneous in density, and in the following examples, it has its own elasticity.

Most manufacturers use a simple soil or rock base, but this leads to local or global deformation of the finished product, or at least the formation of zones with local internal stresses, or even zones with a broken connection.

Thus, in real conditions, the welded joint obtained with good quality is immediately violated, as a result of which it is not possible to create portions of the plate area with equivalent joint parameters.

We propose to dissipate the residual kinetic energy of the connected plates, at least one of the additional layers due to their deformation or destruction, as shown in figure 2.

Thus, the first easily deformable LDP layer provides the quality of the actual connection (welding) of the plates, as it compensates for the elastic deformation during welding.

The subsequent denser and more viscous additional damping interlayers (hereinafter referred to as DDP) of artificial material compensate for the plastic deformation of the finished joint (and the workpiece as a whole), since the kinetic energy of the plates is not spent on deformation of the workpiece, but on the deformation and destruction of the second and subsequent interlayers of DDP .

DDP repeats the shape of the welded plates, which allows you to maintain the shape of the plates and avoid local kinks.

As DDP, you can use wood-particle or fiber boards, drywall, specially compacted sand and combined mixtures and their combinations. The material, size and quantity of the road traffic police are selected empirically.

In total, the set of LDP, DDP and the supporting platform forms a multilayer damping agent.

The use of the above damping means allows you to absorb excess energy and achieve an energy balance between the input and absorbed energy to obtain a strictly metered plastic deformation of mating metals with significantly different melting points and to obtain bimetal with guaranteed high strength and weld quality characteristics uniformly distributed over the entire area of the bimetal sheet .

The method is illustrated by drawings, where in Fig.1 schematically shows the relative placement of the welded plates and damping means; figure 2 schematically shows the mutual placement of the welded plates and a multilayer damping means.

It should be noted that the drawings show only those details that are necessary for understanding the essence of the proposal, and the accompanying equipment, well known to specialists in this field, is not presented in the drawings.

The following positions are affixed to the drawings:

1 - reference platform;

2 - easily deformable layer of the LDP;

3 - fixed plate;

4 - the gap between the plates;

5 - throwing plate;

6 - explosive explosive;

7 - additional damping layer of DDP.

The method is as follows.

To obtain a bimetallic billet, a damping means is made up of a support pad 1 and an easily deformable layer 2 (Fig. 1). First, a support platform 1 is formed. An easily deformed layer 2 is laid on the support platform 1. Then a fixed (clad) plate 3 is installed on it. A throwable (movable) plate 5 and an explosive layer 6 are placed over the plate 3 with a gap of 4. Then, the layer is detonated. explosive 6.

For the manufacture of a multilayer damping means between the supporting platform 1 and the easily deformable layer 2, at least one additional damping layer 7 is placed (Fig. 2).

The method is illustrated by the following examples.

Example 1

A support pad is made of wet sand compacted by a vibrator. An easily deformable layer of LDP made of polyethylene foam 2 mm thick is laid on the supporting platform. Then, a fixed (clad) carbon steel plate with a thickness of more than 25 mm is installed on the LDP, which is not at risk of extensive deformation. Above it, with a gap, a throwable movable plate with a thickness of 3 mm and a layer of explosive explosive are placed. Detonate the explosive layer.

Example 2

A support pad is made of wet sand compacted by a vibrator. An additional damping layer of fiberboard made of chipboard with a thickness of 22 mm is laid on the supporting platform. An easily deformed layer of LDP made of 2 mm thick polyethylene foam is placed on the fiberboard. Then, a fixed (clad) carbon steel plate with a thickness of less than 25 mm is installed on the LDP, which is at risk of extensive deformation. Above it with a gap place a throwable (movable) plate 10 mm thick and a layer of explosive explosives. Detonate the explosive layer.

Example 3

A massive steel support pad is made. An easily deformable layer of LDP made of polyethylene foam 2 mm thick is laid on the supporting platform. Then, a fixed (clad) plate of carbon steel 50 mm thick is installed on the LDP. Above it, a throwable (movable) plate of durable aluminum-magnesium alloy AMg6 12 mm thick and a layer of explosive explosive are placed with a gap. Detonate the explosive layer.

Due to the sharp compression of the LDP between the supporting platform and the fixed (clad) plate, self-ignition of the LDP occurs. LDP combustion products form a “gas damper”, which prevents a sharp collision of the fixed and throwing plates, which prevents extensive melting of AMg6 and ensures a solid high-quality connection.

Previously, the connection of the AMg6 alloy with steel was carried out only through a layer of soft pure aluminum with a thickness of 2–3 mm.

The high quality level of bimetallic billets obtained by the claimed method is confirmed by the conclusions of expert organizations: Central Research Institute of Ferrous Metallurgy named after I.P. Bardina, FSUE Central Research Institute of Structural Materials "Prometheus".

Claims (3)

1. A method of manufacturing by explosion welding of a flat bimetallic billet, comprising installing with a clearance of the throwing plate above the fixed plate and initiating a charge of the explosive located above the throwing plate, using means to reduce the speed of plastic deformation of the plates, characterized in that the speed of plastic deformation is reduced by damping means, which is placed under a fixed plate, consisting of an easily deformable layer having the property of one-sided inelastic deformation, and an artificial supporting platform made of a material with a uniformly distributed density exceeding the density of an easily deformable layer. 2. The method according to claim 1, characterized in that they use an easily deformable layer having the ability to change the state of aggregation under pressure. 3. The method according to claim 1, characterized in that at least one additional damping layer is placed between the easily deformable layer and the supporting platform.

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